[1] A developing apparatus (process unit) including a developer transport body has conventionally been known. The developer transport body includes a substrate having a transport surface disposed to face a latent-image forming surface, which is a surface of a latent-image carrying body and on which an electrostatic latent image is formed by means of electric potential of the surface; and a plurality of electrodes disposed on the substrate.
In such a developing apparatus, an electric field directed toward a predetermined developer transport direction is formed on the transport surface through application of voltages to the electrodes. Thus, a charged developer (toner) on the transport surface moves along the transport surface in the developer transport direction. When the developer reaches a developing area in the vicinity of the latent-image forming surface, the developer is caused to move toward the latent-image forming surface by means of an electrostatic force which is produced through interaction between a charge (charge amount) of the developer and an electric field generated by a difference (difference in electrical potential) between the electrical potential of the latent-image forming surface and that of the transport surface. As a result of the developer having reached the latent-image forming surface and adhering thereto, an image in the developer is formed (developed) on the latent-image forming surface (see, for example, Japanese Patent Application Laid-Open (kokai) No. S59-181375).
Incidentally, when the developer moves from the transport surface to the latent-image forming surface, the developer receives a force (disturbing force), other than the above-mentioned electrostatic force, which is produced by a flow of air or the like. If such a disturbing force is sufficiently smaller than the electrostatic force, the developer can easily move in the direction of the electrostatic force. In such a case, the developer can be caused, without fail, to reach proper positions on the latent-image forming surface in accordance with the electric potential thereof, whereby the quality of an image formed by the developer can be improved. Therefore, conceivably, sufficiently increasing the absolute value (magnitude) of the charge amount of the developer is desired so as to sufficiently increase the electrostatic force.
However, the greater the absolute value of the charge amount of the developer, the greater the risk of the developer adhering to the transport surface due to image force, etc., or the developer aggregating. Therefore, the greater the absolute value of the charge amount of the developer, the greater the possibility that the developer on the transport surface is not transport smoothly. As a result, the developer is non-uniformly distributed in the developing area, whereby the quality of an image formed on the latent-image forming surface may deteriorate.
[2] Many mechanisms for transporting toner (developer) in an image forming apparatus by use of a traveling-wave electric field are conventionally known (as disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. S63-13074, Japanese Patent Publication (kokoku) No. H5-31146, and Japanese Patent Application Laid-Open (kokai) Nos. 2002-351218, 2003-15417, 2004-157259, 2005-275127, etc.) In such a mechanism, a large number of strip-shaped electrodes are juxtaposed in a row on an electrically insulative base plate.
In such a mechanism, polyphase AC voltages are sequentially applied to the plurality of strip-shaped electrodes, whereby a traveling-wave electric field is generated. By the action of the traveling-wave electric field, the above-described toner in a charged state is transported in a predetermined direction.
The above-described mechanism which can transport a charged developer by means of a traveling-wave electric field (hereinafter referred to as an “electric field developer transport apparatus” in some cases) has the following problem. When the developer is not smoothly transported in a certain region on the base plate, the developer may stagnate in that region for a long period of time. This stagnation of the developer may cause adhesion of the developer to the base plate and/or scattering of the developer to the outside.